Engine timing strategies are generally known for controlling engine timing to obtain desirable engine operational characteristics. For example, it is known to retard engine timing to provide torque management in a traction control system or to retard engine timing to prevent engine detonation or knock. See U.S. Pat. Nos. 5,265,693 and 5,235,952, respectively. Similarly, it is known to retard engine timing in response to engine temperature to prevent overheating of the engine or to advance engine timing to improve startability of an engine during cold starts. See U.S. Pat. Nos. 5,201,284 and 5,048,486, respectively. Another engine timing strategy is known for controlling engine timing as a function of engine rotational speed and throttle opening degree for engine cold and warm-up states. See U.S. Pat. No. 5,027,771.
While the above engine timing strategies permit desirable engine operation for the described operating parameters, specifically torque management in a traction control system, reduction of engine knock and prevention of overheating and improved starting, they do not address the need for continuously controlling engine timing as a function of engine speed and intake air temperature to reduce engine emissions or to reduce fuel consumption.
For example, engine brake specific fuel consumption and engine NOx emissions generally decrease with decreasing intake air temperatures. However, a typical engine timing strategy varies engine timing as a function of engine speed irrespective of the engine intake air temperature. As a result, the lower NOx emissions and reduced fuel consumption available at the cooler intake air conditions cannot be obtained with present timing strategies.
Additionally, exhaust temperatures and turbocharger speeds increase with increasing ambient air temperatures and intake air temperatures. Therefore, a need exists for controlling engine timing as a function of engine intake air temperature to maintain exhaust temperatures and turbocharger speeds within acceptable limits.
Conversely, peak cylinder pressures increase with decreasing ambient air temperatures and intake air temperatures. Therefore, a need exists for controlling engine timing as a function of engine ambient or intake air temperature to maintain peak cylinder pressures within acceptable limits.